Glaucoma is the name given to a group of eye diseases in which the optic nerve at the back of the eye is slowly destroyed. In some people, the damage may be caused by poor blood supply to the vital optic nerve fibers, a weakness in the structure of the nerve, or a problem in the health of the nerve fibers themselves. However in most people, this damage is the result of a reduction or blockage of circulation of aqueous or its drainage, known as open-angle glaucoma. As illustrated in FIG. 1, aqueous humor 10 flows through the inside of the eye 12 and nourishes the lens 14, the iris 16, and the inside 18 of the cornea 20. The aqueous humor 10 leaves the cornea 20 and enters into the trabecular meshwork 22, which is the eye's “drain.” The trabecular meshwork 22 contains tiny holes or passages 24 that surround the iris 16. Normally, the aqueous 10 flows freely through the trabecular meshwork 22 and into Schlemm's canal 26, where it then enters back into the bloodstream. However in open-angle glaucoma, if the trabecular meshwork 22 becomes clogged, more aqueous humor 10 flows into the eye 12 than can freely drain out. As a result, intraocular pressure (IOP) can rise, causing ocular hypertension (OHT). OHT is an important risk factor for glaucoma, although other risk factors can contribute to glaucoma, including reduced blood flow to the affected area of the optic nerve.
It is important to reduce elevated IOP as quickly as possible after diagnosis to either prevent the onset of glaucoma or if glaucoma has already damaged the optic nerve and caused vision loss, to prevent any further damage and vision loss. The importance of lowering IOP to treat glaucoma is known. (See, Taban et al., The Importance of Lowering Intraocular Pressure, Medscape Ophthalmology, Feb. 20, 2008) Once IOP is lowered, a suitable treatment is selected to keep IOP under control at normal levels. Known treatments include medication, laser treatment, and surgery. Patient factors such as age, general health, and stage of glaucoma, as well as various socioeconomic and technologic factors may lead to different recommendations for different patients. In the case of medication, eyedrops and pills are the most common treatments. Both can be used to decrease the production of aqueous humor in the eye, but side effects can occur, including headaches, eye irritation, and/or blurred or dimmed vision. Further, the effectiveness of medication diminish over time.
Laser treatment known as “trabeculoplasty” is another accepted procedure for treatment of open-angle glaucoma if medications inadequately control IOP levels. This procedure is commonly performed using either a cw argon laser or a cw diode laser. In this procedure, the laser energy is delivered gonioscopically using a contact goniolens. As illustrated in FIG. 2, laser energy 28 emitted from a laser (not shown) is focused onto a small diameter spot 30 on the trabecular meshwork 22. The laser energy 28 heats the meshwork tissue 32 until a white spot (or laser burn) is created. It is generally accepted that the laser burns cause shrinkage in the trabecular meshwork tissue 32. This shrinkage is believed to cause the meshwork tissue 32 disposed between the laser burns to stretch and become more open, thereby decreasing the resistance of the trabecular meshwork 22 to aqueous humor outflow thus reducing IOP. If effective, trabeculoplasty may reduce IOP by twenty to twenty-five percent. (See Taban et al., The Importance of Lowering Intraocular Pressure, Medscape Ophthalmology, Feb. 20, 2008)
Several issues can exist with laser trabeculoplasty. One issue is that the IOP lowering effect tends to disappear over time. IOP may only be adequately controlled for just a few years. Successive treatment may be limited without risking coagulative damage to the trabecular meshwork. Another issue that may be encountered with laser trabeculoplasty is pressure spiking. In the days following the trabeculoplasty procedure, the patient's IOP can rise above pretreatment levels. This pressure spiking requires careful monitoring and control. Other complications include iritis, hyphema, and development of peripheral anterior synechiae.
Another accepted method for treatment of open-angle glaucoma is invasive surgery. Trabeculectomy and tube shunts are the most typical procedures performed. In trabeculectomy, the surgeon removes a section of the limbal tissue underneath a scleral flap to create a path for aqueous humor to drain out of the eye and into a bleb formed by the conjunctiva to reduce IOP. Complications that can occur from trabeculectomies including hypotony, flat chambers, chorodial effusions, suprachoroidal hemorrhages, elevated IOP, hyphema, cataract, and infection. Tube shunts are most commonly used in open-angle glaucoma if trabeculectomy has failed. A tube is placed in the anterior chamber that allows aqueous humor to flow to an extraocular reservoir secured near the equator on the sclera to reduce IOP. Complications of tube shunts include overfiltration, tube-cornea touch, tube obstruction, tube erosion, tube migration, and ocular motility disorders. Other less common surgical interventions include ciliary body abalation, endocyclophotocoagulation, or cyclecryotherapy.
There exists a need to provide a non-invasive method, apparatus, and system for treating open-angle glaucoma which results in longer term IOP control and without side effects or issues that can arise from known methods, including medication, laser treatment, and surgery.